This invention relates to an apparatus for measuring heat flow from a surface, and more particularly, to a free standing apparatus for measuring heat flow from a surface.
With the cost of energy continuing to rise, and with resources for the production of energy getting scarcer by the minute, heat loss has become a major concern for the industrial world as well as for individuals. As a result, much research and development has been done over the past few years in the study of detecting and measuring heat loss.
In detecting and measuring heat loss, it is sometimes necessary to take heat flux readings from a specified point. One device used in the collection of flux readings is a portable heat fluxmeter fixture described in U.S. Pat. No. 4,589,781. The device of U.S. Pat. No. 4,589,781 is used in processes for heat loss surveys and quantifying heat loss from surfaces. The device of U.S. Pat. No. 4,589,781 consists of a hand held portable fixture with a handle suitable to be grasped and held by an operator. On the device, there is a constant force spring which resists the application of the device so that the force being applied to the test surface is approximately the same each time it is used. With a thermal fluxmeter being attached to one end of this device, a heat flux reading is obtained from the fluxmeter. The heat flux reading is then used as a key parameter in data reduction in a heat loss survey method.
The portable heat fluxmeter fixture of U.S. Pat. No. 4,589,781 has functioned quite accurately when applied to industrial process surfaces, where surface temperatures are relatively high in comparison to "ambient." However, the potential for error increases when the technology is applied to low temperature surfaces, like buildings.
For example, when using the portable heat fluxmeter fixture of U.S. Pat. No. 4,589,781 on low temperature surfaces, it has been discovered that the body temperature of a fluxmeter operator affects results. When the body temperature of the operator is higher than the surface the operator is standing next to, testing measured heat flow patterns reveal that heat flow decreases (sometimes actually reverses) through the region where the heat flow is measured. Therefore, it is difficult to get consistent fluxmeter readings on low temperature surfaces.
A means for applying a constant force to the fluxmeter of U.S. Pat. No. 4,589,781 which is necessary for accurate and repeatable readings is imperfect because a load is not always repeatable due to friction hysteresis. This problem is complicated by the fact that no means is provided for actually measuring the load.
It is desirable to provide a fluxmeter which contains a reduced cross-section of the legs in order to minimize disturbances to air flows over the surface of the fluxmeter which, in turn, better simulates "normal" or unmetered conditions. It is also desirable to provide a fluxmeter with reduced thermal conductivity of the legs. Besides helping to minimize the inducement of unnatural heat flows which adversely effects accuracy, low conductivity and small crosssection legs would help heat flows to stabilize more quickly, allowing accurate measurements to begin soon after the fluxmeter is applied to the surface.
Even with small fluxmeters normally employed, loads as high as fifteen pounds may be required for good accuracy. Fluxmeters heretofore have required an operator to manually maintain this load for more than a minute resulting in muscle fatigue and other discomforts which often cause errors through shaking or movement of the fixture which, in turn, causes the load and/or contact area to vary.
A problem associated with heat loss survey methods employing pyrometers is that contact surface pyrometers often provide erroneous data. Since an accurate spot sample of surface temperature is as important as accurate fluxmeter readings, it is desirable to improve this parameter, as well.
Also, manually holding a portable fluxmeter such as described in U.S. Pat. No. 4,589,781 next to a surface being tested, has a drawback in that, if a test surface generates an unbearable temperature, an operator may not be able to withstand the temperature for a long enough period of time to get a good fluxmeter reading. Therefore, in some instances, the portable fluxmeter fixture of U.S. Pat. No. 4,589,781 is inapplicable. Furthermore, the test site may contain hazards other than heat--noise, for example - which may make extended human presence uncomfortable or dangerous.
In addition, when using the fluxmeter fixture of U.S. Pat. No. 4,589,781, it is difficult and almost impossible to access some surfaces in order to take a fluxmeter reading. Sometimes an operator is too short, and in other cases an operator cannot squeeze into a small opening in order to get close enough to take a reading.
In heat loss survey methods using hardware such as described in U.S. Pat. No. 4,589,781, it is found that accuracy suffers when the technology is applied in situations where there is a very small temperature difference between the measured surface and the surroundings.
Therefore, it is desired to provide an apparatus which alleviates much of the error in these low temperature difference applications. The apparatus is useful in any case where accurate heat fluxmeter readings are required, where there are only small temperature differences between the surface and the surroundings, and where a permanently mounted fluxmeter is not desirable.